The present invention relates to a blade for a gas turbine engine, and more particularly, to such a blade having a dovetail portion which exhibits improved resistance to blade pull-out.
Gas turbine engine blades are generally provided with dovetail portions which matingly engage corresponding dovetail slots in circumferential retaining members. Exemplary blades having such a dovetail portion for mating with such a dovetail slot are described in U.S. Pat. No. 3,734,646, entitled, "Blade Fastening Means," issued May 22, 1973, to Perkins, and U.S. Pat. No. 4,265,595, entitled, "Turbomachinery Blade Retaining Assembly," issued May 5, 1981, to Bucy, et al. One attractive feature of these exemplary blades is that individual ones of such blades may be removed or installed. These Patents are assigned to the assignee of the present application and are hereby incorporated into reference herein.
Such conventional blade and blade fastening systems are satisfactory for many applications. However, under certain conditions, conventional blade dovetail configurations exhibit insufficient resistance to blade pull-out forces. For example, substantial blade pull-out forces are expected in the form of conventional gas turbine engine generally referred to as a turbofan engine. A conventional turbofan engine includes a fan section, a compressor section, a combustor section, a high pressure turbine section, a low pressure turbine section, and an exhaust section. Such turbofan engines typically have relatively large fan blades which are exposed to damage which may be caused by foreign objects such as birds and the like. For example, if a bird strike situation is of sufficient severity, one or more of the fan blades, or portion(s) thereof, may be released from mating engagement with its retaining dovetail slot in the fan disk. Such a situation may result in a failure mode in which the blade trailing the released blade may be pulled out of its dovetail slot by its interaction with the released blade. In this connection, the moments and loading resulting from the impact interaction, combined with the operational centrifugal loading of the trailing blade, can be sufficient to shear out the trailing blade dovetail, thereby causing further damage to the trailing blade as well as likely further damage to other fan blades and associated engine hardware, such as bearings, seals, and structural frames.
In view of the foregoing, it is desirable to improve the dovetail resistance to such blade pull-outs. One simple solution to this problem is to provide a deeper and larger blade dovetail configuration. However, this simple solution thereby requires a deeper dovetail slot and heavier fan disk member. Such additional bulk, although desirable for strength purposes, is undesirable for cost and fuel efficiency purposes. Indeed, the use of bulkier blade dovetail and disk members additionally requires a heavier disk and bearing structure to accommodate the larger loadings which are associated with the deeper blade dovetails. Furthermore, this simple solution requires dovetail disk configurations in existing engines to undergo substantial modification to provide the improved pull-out resistance. Thus, it would be desirable to provide a simple means for improving the blade dovetail pull-out resistance.
Accordingly, it is a general object of the present invention to provide a gas turbine engine blade having a dovetail portion which exhibits improved strength.
It is another object of the present invention to provide such a blade having a dovetail portion which exhibits improved resistance to blade pull-out forces.
It is another object of the present invention to provide such a blade which does not require a deeper dovetail to provide such improved resistance.
It is another object of the present invention to provide such a blade which can be used to simply replace or repair existing blades having insufficient resistance to blade pull-out forces.
It is another object of the present invention to provide such a blade which is compatible with single blade removal/installation.
It is another object of the present invention to provide such a blade which is relatively simple to manufacture.